Ion exchange resins are widely used in the production of highly pure water in the nuclear, electronics (semi-conductor), pharmaceutical and food industries. In the nuclear industry, for example, ion exchange resins are used for purification of nuclear process water.
The problem exists that commercial grade ion exchange resins contain varying quantities of organic and inorganic impurities which have a tendency to leach out of the resin during use. Many of these impurities arise during manufacture of the resin, and include monomers and oligomers of the polymer from which the resin beads are formed, as well as impurities in the starting materials. These impurities may become functionalized, for example, with sulphate or amino groups during functionalization of the resin.
Due to the presence of leachable impurities, commercial ion exchange resins must be treated prior to use in critical applications where extraneous organic materials are unacceptable. Presently used purification methods include a variety of proprietary techniques, most of which are based on extraction of leachable impurities by organic solvents. In one of these methods, the resin is washed with a series of solvents of decreasing polarity. In addition to being slow, costly and wasteful, this process suffers from a number of other disadvantages. Firstly, it is not very effective. Organic solvent molecules are relatively bulky and cannot effectively penetrate into the interior of the cross-linked resin beads to leach out the impurities contained therein. Secondly, solvent treatments may require high temperatures and pressures, which may damage the integrity of the resin beads, for example by de-crosslinking, or facilitating loss of functional groups. Thirdly, the organic solvents used to wash the resin may be absorbed by the resin beads, resulting in further contamination.
Therefore, there is a need for a more economical and effective method for removing leachable impurities from commercial ion exchange resins.